Our Gemara on Amud Beis discusses the obligation to cite sources when quoting a teaching. But there is a chain of at least three scholars, such as, “rabbi so and so, in the name of rabbi so and so, in the name of rabbi so and so”, it is permissible to quote the first and last source, without stating the middle sources. 

Presumably, the point of quoting the first and last source is to provide basic verification by preserving the original and final rabbis in the chain of tradition. However there is more to the story. There is a mystical power to quoting another person’s Torah, as the Gemara (Yevamos 96a) tells us:

אָמַר רַבִּי יוֹחָנָן מִשּׁוּם רַבִּי שִׁמְעוֹן בֶּן יוֹחַי: כׇּל תַּלְמִיד חָכָם שֶׁאוֹמְרִים דְּבַר שְׁמוּעָה מִפִּיו בָּעוֹלָם הַזֶּה, שִׂפְתוֹתָיו דּוֹבְבוֹת בַּקֶּבֶר. אָמַר רַבִּי יִצְחָק בֶּן זְעֵירָא, וְאִיתֵּימָא שִׁמְעוֹן נְזִירָא: מַאי קְרָאָה — ״וְחִכֵּךְ כְּיֵין הַטּוֹב הוֹלֵךְ לְדוֹדִי לְמֵישָׁרִים דּוֹבֵב שִׂפְתֵי יְשֵׁנִים״.

Rabbi Yoḥanan said in the name of Rabbi Shimon ben Yoḥai: With regard to any Torah scholar in whose name a matter of the tradition is said in this world, his lips mouth the words in the grave, as though he is talking. Rabbi Yitzḥak ben Ze’eira said, and some say this was stated by Shimon the Nazirite: What is the verse from which it is derived? “And the roof of your mouth is like the best wine that glides down smoothly for my beloved, moving gently the lips of those who are asleep” (Song of Songs 7:10).

In Sha’are Siach (a contemporary sefer that relates extemporaneous discussions and questions with Rav Chaim Kanievsky, ZT”L) Rav Kanievsky was asked if the idea that the lips of the deceased recite the Torah that is quoted is limited to their chiddushim, that is their original insights and teachings, or it includes any Torah that they taught. Rav Chain held that only their original teachings have a sufficient spiritual connection to the person to cause the effect of arousing them up through their teachings. Rav Chaim in Sha’are Emunah (Mishna Pesh 2:6, Seif 14) proves his assertion from our Gemara.  Why is it sufficient to quote only the first and last rabbi in the chain?  We quote the original teacher since it is his chiddush, and we want to achieve the effect of arousing his lips to say his Torah, even from the grave. We quote the last person in the chain out of respect, because the last person, from whom we directly heard the teaching, has a status of a rebbe.

The Chidah (Chomas Anakh, Tehilim 40) discusses if a person who writes a Sefer anonymously benefits from this effect or not, since his name is not mentioned albeit people are still studying his Torah. Chidah asserts that even an anonymous Sefer achieves the same effect for the author, as Hashem knows who taught this Torah, even if others do not know. Why then is there an obligation to quote a teaching’s source? Chidah says this is for the practical reason that if the source is known it will be more respected, therefore it encourages more people to study it.

Elsewhere, the Chidah (Rosh Dovid, Chukas) seems to argue on Rav Chaim’s point. He argues that the Gemara’s phrase is “Shemuah” “oral teaching “. It would seem that the point is the teaching of a tradition, and not so much a chiddush. Thus anyone cited along the chain will be revived when the teaching is repeated by a subsequent student. 

I believe the difference between Rav Chaim and the Chidah depends on the following chakirah (analysis): We can theorize the basic reason behind this idea that studying another person’s Torah arouses them in the grave is that the person’s soul contains the sum total of the Torah they absorbed. By studying their Torah, a living part of them is channeled and activated. We might wonder what happens when Torah is studied and absorbed by the soul? Is it a special life force coming from something new that the person created, a new insight in Torah that now somehow merges with the person’s consciousness and becomes immortal? Or perhaps we can say that any Torah learned well, becomes intertwined with the person’s soul, even if it is not a new idea or creation. This latter position would be aligned with the Chidah, thus any Torah said over that was once studied by the person becomes an activator of their soul.  However, Rav Chaim’s position is consistent with the former idea. Only original and creative Torah thoughts are attached to the person’s soul to the extent that only Torah of that degree achieves this effect.